In recent years, for the purpose of weight saving and an improvement in mechanical strength, composite fiber-reinforced resins obtained by impregnating reinforcing fiber substrates such as carbon fiber and glass fiber with a resin have been widely utilized in a variety of fields and uses and their application to aircraft components and automobile components have been in progress. Such fiber-reinforced resin molded articles are required to have less defects such as voids, the impregnation of the reinforcing fiber substrate with the resin being performed at a predetermined fiber volume content, so as to exhibit predetermined properties such as mechanical strength. Also, it is required to have such shaping ability that molding is possible even if the shape is complex one. For such requirement, there have been proposed a variety of fiber-reinforced resin intermediate materials wherein a reinforcing fiber substrate is impregnated with a resin and which is used under heating and pressurization in a laminated state.
PTL 1 proposes a fiber-reinforced thermoplastic resin sheet wherein, although a thermoplastic resin has high melt viscosity and uniform impregnation of a reinforcing fiber bundle therewith is difficult to perform, a thermoplastic resin non-woven fabric is melted to impregnate the reinforcing fiber bundle with the thermoplastic resin by overlaying the thermoplastic resin non-woven fabric on a reinforcing fiber sheet in which a plurality of the reinforcing fiber bundles are aligned in one direction and performing pressurization while heating. It is said that the fiber-reinforced thermoplastic resin sheet can be made such a semi-impregnated state that void space parts at which the reinforcing fiber bundle is not impregnated with the thermoplastic resin are present. Therefore, it is said that a time required for manufacturing the fiber-reinforced thermoplastic resin sheet can be shortened, a fiber-reinforced thermoplastic resin sheet having flexibility is obtained, non-impregnated parts can be reduced since the reinforcing fiber sheet can be thinned, and thus it is possible to perform sufficient impregnation when the pressurization while heating is performed at the time of processing into a final molded article.
PTL 2 proposes a prepreg which comprises a fiber substrate formed in a layered shape and a resin layer provided on at least one surface side of the fiber substrate and composed of a resin composition and wherein a void space layer not impregnated with the resin composition is formed in at least a part of the fiber substrate. It is said that the void space layer of the prepreg may have a form that a part of the fiber substrate is exposed and is preferably formed so as to communicate from one end of the prepreg to another end thereof. Moreover, it is said to be sufficient that a void space layer communicating from one end to the other end is present at an intermediate part thereof even when resin layers are present on both surfaces of the fiber substrate. In the case of laminating such a prepreg, since the resin is supported with the fiber substrate, it is said that the fiber substrate can be prevented from waving and air is easily released at the time of laminating the prepreg and air bubbles are less prone to occur. As the above resin composition, a thermosetting resins such as a phenol novolak resin and a cresol novolak resin are mentioned and a thermoplastic resin such as a phenoxy resin or a polyimide resin may be used in combination.
PTL 3 proposes a notched prepreg substrate having reinforcing fibers aligned in one direction, wherein a plurality of rows composed of intermittent notches in a direction crossing the reinforcing fibers are provided on the whole surface of the prepreg substrate, projection length of the notches projected to a perpendicular direction of the reinforcing fibers is 30 μm to 10 mm, all of the reinforcing fibers are substantially cut by the notches, fiber length of the reinforcing fiber cut by the notches is 10 to 100 mm, and fiber volume content falls within the range of 45 to 65%. It is said that the notched prepreg substrate has good flowability, has molding followability, is excellent in shaping ability, and can provides a prepreg substrate that is an intermediate substrate for fiber-reinforced plastics suitably used in automobile components, sporting goods, and the like.